Device for treating human skin by means of radiation

ABSTRACT

The invention relates to a device ( 1 ) for treating human skin by means of radiation. The device comprises a housing ( 3 ) with a radiation exit opening ( 13 ). A radiation source ( 9 ) is accommodated in the housing. Radiation generated by the radiation source propagates from the radiation source towards the radiation exit opening via a radiation path ( 15 ) comprising a radiation filter having a predetermined transmission spectrum. According to the invention the radiation filter comprises a reflecting surface ( 23 ) via which the radiation propagating along the radiation path ( 15 ) is reflected. The reflecting surface has a coating which provides the reflecting surface with a reflection spectrum substantially matching the predetermined transmission spectrum. An advantage is that the reflection surface can be optimally and uniformly cooled, so that the heat generated as a result of the absorption of part of the radiation by the radiation filter can be effectively transmitted to a cooling system ( 25 ) of the device ( 1 ). In a particular embodiment the device ( 1 ) is an epilator for removing hairs from the human skin and the radiation source ( 9 ) is a flash lamp. The radiation path ( 15 ) is enclosed by a channel ( 17 ) having a bend ( 19 ) and having an inner wall ( 21 ) on which the reflecting surface ( 23 ) is provided.

The invention relates to a device for treating human skin by means ofradiation, which device comprises a housing with a radiation exitopening, a radiation source accommodated in the housing, and a radiationpath between the radiation source and the radiation exit opening, saidradiation path comprising a radiation filter having a predeterminedtransmission spectrum.

A device for treating human skin of the kind mentioned in the openingparagraph is known from U.S. Pat. No. 6,280,438 B1. The known device isused to remove hairs from human skin by means of light pulses having arelatively high energy density. The radiation source is a gas-filledlinear flash lamp which is arranged in the focus of an ellipticalreflector and generates pulsed light having a relatively broad spectrum.The radiation filter is a plate-shaped filter which is arranged in theradiation path transversely to a main direction of the radiation pathand covers the radiation exit opening, so that the light generated bythe flash lamp passes through the filter. The transmission spectrum ofthe radiation filter is such that the filter transmits the portion ofthe spectrum of the generated light which is effective for the removalof the hairs and which has no unwanted side effects on the skin, andabsorbs the portion of the spectrum of the generated light which wouldhave unwanted side effects on the skin. In this manner the hairs areremoved in an effective manner, while side effects on the skin, such asburns, are prevented as much as possible.

As a result of the absorption by the radiation filter of said portion ofthe spectrum of the generated light, the filter is heated. Since thegenerated light pulses have a relatively high energy density, arelatively large amount of energy is absorbed by the radiation filter. Adisadvantage of the known device for treating human skin is that theradiation filter is cooled only to a limited extent, because only acircumferential portion of the filter is in direct thermal contact withthe housing of the device. As a result, during operation excessivethermal deformations of the filter occur, which can lead to permanentdeformations or even fracture of the filter.

It is an object of the invention to provide a device for treating humanskin as mentioned in the opening paragraph having a radiation filterwhich can be better cooled, so that the risk of permanent deformationsor fracture of the filter is limited.

In order to achieve this object, a device for treating human skin inaccordance with the invention is characterized in that the radiationfilter comprises a reflecting surface via which the radiationpropagating along the radiation path is reflected and which has acoating providing the reflecting surface with a reflection spectrumsubstantially matching the predetermined transmission spectrum. In thedevice for treating human skin in accordance with the invention theradiation generated by the radiation source is filtered as a result ofthe predetermined reflecting properties of said reflecting surface. Aportion of the spectrum of the generated radiation, which is effectivefor the intended treatment of the human skin and which has no unwantedside effects on the skin, is reflected by said reflecting surface, whilea portion of the spectrum of the generated radiation, which would haveunwanted side effects on the skin, is absorbed by said reflectingsurface. The reflecting surface is arranged adjacent the radiation pathand bounds the radiation path in such a manner that at least asubstantial portion of the radiation is reflected once or, preferably,more than once by the reflecting surface while propagating from theradiation source towards the radiation exit opening. The reflectingsurface does not need to be transparent to the radiation. As a resultall portions of the reflecting surface can be brought into directthermal contact with a cooling system of the device, so that an improveduniform thermal contact is achieved between the reflecting surface andthe cooling system of the device. In this manner, thermal deformationsof the reflecting surface are limited and local excessive thermaldeformations of the reflecting surface are even prevented, so thatpermanent deformations and fracture of the radiation filter areprevented.

A particular embodiment of a device for treating human skin inaccordance with the invention is characterized in that the radiationfilter comprises a channel which encloses the radiation path and whichcomprises an inner wall on which the reflecting surface is provided. Inthis embodiment the radiation propagates from the radiation sourcetowards the radiation exit opening through said channel. Since thereflecting surface is provided on the inner wall of said channel, theradiation propagating through the channel will be reflected by thereflecting surface. In this manner the radiation filter is veryeffective, and the filter has a practical structure.

A further embodiment of a device for treating human skin in accordancewith the invention is characterized in that the channel comprises a bendsituated between the radiation source and the radiation exit opening. Asa result of the presence of said bend in the channel, all portions ofthe radiation propagating through the channel are forced to strike theinner wall of the channel on which the reflecting surface is provided.As a result, all portions of the radiation propagating through thechannel are reflected by the reflecting surface once or even more thanonce, so that the effectiveness of the filter is further improved.

A particular embodiment of a device for treating human skin inaccordance with the invention is characterized in that the reflectingsurface comprises a first portion, which has a first coating materialproviding said first portion with a first reflection spectrum, and asecond portion, which has a second coating material providing saidsecond portion with a second reflection spectrum, said first and saidsecond reflection spectrum together matching the predeterminedtransmission spectrum. For most treatments of the human skin, such asthe removal of hairs from the human skin, the predetermined transmissionspectrum of the radiation filter should be such that a first portion ofthe radiation having wavelengths below a first limit are absorbed by thefilter, that a second portion of the radiation having wavelengthsbetween said first limit and a second limit above said first limit istransmitted by the filter, and that a third portion of the radiationhaving wavelengths above said second limit is absorbed by the filter. Inthis particular embodiment such a profile of the transmission spectrumis achieved in a practical manner if the first reflection spectrum issuch that the first portion of the reflecting surface substantiallycompletely absorbs radiation having wavelengths below said first limitand substantially completely reflects radiation having wavelengths abovesaid first limit, and if the second reflection spectrum is such that thesecond portion of the reflecting surface substantially completelyreflects radiation having wavelengths below said second limit andsubstantially completely absorbs radiation having wavelengths above saidsecond limit.

A particular embodiment of a device for treating human skin inaccordance with the invention is characterized in that the reflectingsurface is provided on a wall which is in thermal contact with a coolingsystem. A uniform thermal contact is present between the reflectingsurface and said wall. The cooling system can be designed in such amanner that a uniform thermal contact is also present between said walland said cooling system. In this manner, a simple and practicalstructure is achieved to uniformly cool the reflecting surface.

A further embodiment of a device for treating human skin in accordancewith the invention is characterized in that the cooling system comprisesa circuit filled with a cooling fluid, the wall being in thermal contactwith said circuit. As a result of the use of said circuit, the wall andthe reflecting surface provided thereon are uniformly cooled.

A further embodiment of a device for treating human skin in accordancewith the invention is characterized in that the cooling system comprisesa fan for generating a gas stream and a guide for guiding said gasstream along the wall. As a result of the use of said fan and saidguide, the wall and the reflecting surface provided thereon areuniformly cooled.

A particular embodiment of a device for treating human skin inaccordance with the invention is characterized in that the device is adevice for removing hairs from human skin, wherein the radiation sourceis a flash lamp. The light of the flash lamp has a relatively broadspectrum ranging from UV light to near IR light. The portion of thisspectrum, which is effective for the removal of hairs from human skin,lies between approximately 600 nm and 900 nm. The portions of thisspectrum below approximately 600 nm and above approximately 900 nm arenot effective for the removal of hairs and in addition cause unwantedside effects on the skin such as burns or even DNA mutations. The energydensity of the light necessary to remove the hairs is relatively high,so that the radiation filter has to absorb a large amount of energy. Inview of these properties of the light of the flash lamp, the inventionis particularly suitable for use in a device for removing hairs by meansof a flash lamp.

Embodiments of a device for treating human skin by means of radiationaccording to the invention will be described hereafter with reference tothe figures, in which

FIG. 1 schematically shows a first embodiment of a device for treatinghuman skin in accordance with the invention,

FIG. 2 schematically shows a second embodiment of a device for treatinghuman skin in accordance with the invention, and

FIG. 3 schematically shows a third embodiment of a device for treatinghuman skin in accordance with the invention.

The first embodiment of a device 1 for treating human skin is a devicefor removing hairs from human skin, in particular an epilator forremoving the hairs for a relatively long time or even permanently. FIG.1 schematically shows only the main parts of the device 1 which arenecessary to understand the principles of the invention. The device 1comprises a housing 3 having a grip 5 and a head 7 mounted on the grip5. The head 7 accommodates a radiation source 9, which is a gas-filledlinear flash lamp in this particular embodiment. In a front portion 11of the head 7 a radiation exit opening 13 is provided for the lightgenerated during operation by the radiation source 9. The head 7 furtheraccommodates a radiation path 15, which extends between the radiationsource 9 and the radiation exit opening 13. During operation theradiation source 9 generates light pulses having a relatively highenergy density, which propagate from the radiation source 9 towards theradiation exit opening 13 and irradiate the human skin present in frontof the radiation exit opening 13. Part of the light is absorbed by thehair roots and the hair follicles present in the skin, which areconsiderably heated as a result of the relatively high energy density ofthe light. As a result the hair roots and the hair follicles are damagedor even destroyed, so that growing of the hairs is prevented for aconsiderably long time or even permanently.

In the embodiment shown in FIG. 1 the radiation path 15 is enclosed by achannel 17 having a rectangular or square cross section and having abend 19 situated between the radiation source 9 and the radiation exitopening 13. An inner wall 21 of the channel 17 is provided with areflecting surface 23. As a result of the presence of the bend 19 allportions of the light propagating from the radiation source 9 towardsthe radiation exit opening 13 are forced to strike the inner wall 21 andto be reflected at least once by the reflecting surface 23 provided onthe inner wall 21. The reflecting surface 23 has a coating whichprovides the reflecting surface 23 with a predetermined reflectionspectrum. In the embodiment shown in FIG. 1 said coating is a highlyreflective dielectric multilayer mirror coating (Suffix: 503) sold byJML Optical Industries and disclosed on page G-18 of the brochure JMLDirect Optics, third edition. This particular coating has a relativelylow reflection coefficient for wavelengths below approximately 600 nmand above approximately 900 nm. For wavelengths between approximately680 nm and 850 nm this particular coating has a reflection coefficientof approximately 100%. Because the radiation source 9 has a relativelybroad spectrum ranging from UV light to near IR light, the channel 17comprising the reflecting surface 23 does not only define and bound theradiation path 15, but is also effectively used as a radiation filter ofthe radiation path 15 having a predetermined transmission spectrum,wherein the reflection spectrum of the reflecting surface 23substantially matches said predetermined transmission spectrum. In theembodiment of FIG. 1 the radiation filter thus substantially completelytransmits the portions of the light from the radiation source 9 havingwavelengths between approximately 680 nm and 850 nm. These portions ofthe wavelengths are particularly effective for the removal of hairs fromhuman skin without causing inadmissible side effects on the skin. Theradiation filter absorbs a major portion of the light from the radiationsource 9 having wavelengths below approximately 600 nm and aboveapproximately 900 nm. These portions of the wavelengths are noteffective for the removal of hairs and would only cause unwanted sideeffects on the skin such as burns or even DNA mutations. In this mannerthe hairs are effectively removed by the light from the radiation source9, but unwanted side effects of the light on the human skin areprevented as much as possible by the presence of the radiation filter.

The portions of the spectrum of the light from the radiation source 9,which are not reflected by the reflecting surface 23, are absorbed bythe inner wall 21, which is made from a light absorbing material such asblack glass. As a result, the inner wall 21 is heated. Since the lightpulses generated by the radiation source 9 have a relatively high energydensity, a relatively large amount of energy is absorbed by the innerwall 21. An advantage of the use of the reflecting surface 23 as theradiation filter for the generated light is that the reflecting surface23 does not need to be transparent to the radiation in view of itsposition adjacent the radiation path 15. As a result all portions of thereflecting surface 23 can be brought into direct thermal contact with acooling system 25 of the device 1. In the embodiment shown in FIG. 1 thecooling system 25 comprises a circuit 27 filled with a cooling fluid.The circuit 27 is bounded by the inner wall 21 of the channel 23 and byan additional wall 29 arranged parallel to the inner wall 21. The device1 further comprises pumping means not shown in FIG. 1 for pumping thecooling fluid through the circuit 27 and along the inner wall 21. Thusall portions of the inner wall 21 are in direct thermal contact with thecircuit 27 of the cooling system 25. As a result a uniform thermalcontact is provided between the inner wall 21 and the cooling system 25.Since the inner wall 21 is thus uniformly cooled by the cooling system25, thermal deformations of the reflecting surface 23 are limited andlocal excessive thermal deformations of the reflecting surface 23 areeven prevented, so that permanent deformations and damage or fracture ofthe radiation filter are prevented.

It is noted that the position of the reflecting surface 23 relative tothe radiation path 15 should be such that at least a major portion ofthe light generated by the radiation source 9 is reflected once by thereflecting surface 23. Preferably all portions of the generated lightare reflected by the reflecting surface 23, and preferably more thanonce. It will be understood that a person skilled in the art of opticswill be able to establish in a straightforward manner the geometry anddimensions of the channel 17 and the reflecting surface 23 in such amanner that this condition is met. It is noted that the presence of thebend 19 increases the amount of light being reflected by the reflectingsurface 23, so that the effectiveness of the radiation filter isconsiderably improved. However, the presence of said bend 19 is notessential, and sufficient reflecting properties can also be obtained forexample by means of a straight channel having a relatively large ratiobetween its length and width. Further, the invention also includesembodiments in which the radiation filter comprises more than onechannel or a plurality of channels, for example a matrix of channels,provided with reflecting surfaces on their inner walls. It is furthernoted that the effectiveness of the radiation filter of the device 1 isincreased as a result of the use of the channel 17, and that in thismanner the radiation filter has a practical structure. It is noted,however, that the use of the channel 17 or of light guiding channels ingeneral is not essential. The reflecting surface may, for example, alsobe provided on a single wall structure, or on a series of adjacent orconsecutive wall structures, which are in such a position relative tothe radiation path that a substantial portion of the light generated bythe radiation source 9 is reflected by the reflecting surface beforepassing the radiation exit opening.

The second embodiment of a device 31 for treating human skin inaccordance with the invention also is a device for removing hairs fromhuman skin, in particular an epilator for removing the hairs for arelatively long time or even permanently. FIG. 2 schematically showsonly the main parts of the device 31 which are necessary to understandthe principles of the invention. Parts of the device 31 which correspondto parts of the device 1 shown in FIG. 1 and which were discussed in theforegoing are indicated by means of corresponding reference numbers inFIG. 2 and will not be discussed in detail. Hereafter only the maindifferences between the device 31 and the device 1 will be brieflydiscussed.

The device 31 mainly differs from the device 1 in that the device 31comprises a cooling system 33 which is different from the cooling system25 of the device 1. The cooling system 33 comprises a fan 35 which canbe driven by an electric motor not shown in FIG. 2. The channel 17′ isformed by a sheet 37 made from a light absorbing material on which theinner wall 21′ having the reflecting surface 23′ is provided. Duringoperation the fan 35 generates an air stream 39, which is guided along amajor portion of an outer surface 41 of the sheet 37 by means of guidingchannels 43 provided between the sheet 37 and an inner wall 45 of thehead 7′. As the air stream 39 is thus present along a major portion ofthe outer surface 41 of the sheet 37, also in this second embodiment asubstantially uniform cooling of the inner wall 21′ is obtained. Thecooling system 33 has a relatively simple and practical structure.

The third embodiment of a device 51 for treating human skin inaccordance with the invention also is a device for removing hairs fromhuman skin, in particular an epilator for removing the hairs for arelatively long time or even permanently. FIG. 3 schematically showsonly the main parts of the device 51 which are necessary to understandthe principles of the invention. Parts of the device 51 which correspondto parts of the device 1 shown in FIG. 1 and which were discussed in theforegoing are indicated by means of corresponding reference numbers inFIG. 3 and will not be discussed in detail. Hereafter only the maindifferences between the device 51 and the device 1 will be brieflydiscussed.

The device 51 mainly differs from the device 1 in that the geometry andthe dimensions of the channel 17″ of the device 51 and the position ofthe radiation source 9″ are such that all portions of the lightgenerated by the radiation source 9″ are reflected at least twice by theinner walls of the channel 17″, i.e. at least once by an upper innerwall 53 of the channel 17″ and at least once by a lower inner wall 55 ofthe channel 17″. This reflecting property of the channel 17″ is mainlyachieved by means of a relatively large ratio between the length and thewidth of the channel 17″, but it will be understood that a personskilled in the art of optics will be able to establish in astraightforward manner more exact values of the main dimensions of thechannel 17″ by means of which said reflecting property can be achieved.Said upper inner wall 53 comprises a first portion 57 of a reflectingsurface of the channel 17″, while said lower inner wall 55 comprises asecond portion 59 of said reflecting surface. Said first portion 57 andsaid second portion 59 of the reflecting surface are provided withrespectively a first coating material and a second coating material,said first coating material providing said first portion 57 with a firstreflection spectrum and said second coating material providing saidsecond portion 59 with a second reflection spectrum. In the embodimentshown in FIG. 3 said first coating material is a coating material asspecified in the Linos Photonics catalog, 2001, section thin filmcoatings, page H13, item FKP-5. This coating material has a so-callededge wavelength of approximately 600 nm, so that the first coatingmaterial has a relatively low reflection coefficient for wavelengthsbelow approximately 600 nm and a relatively high reflection coefficientfor wavelengths above approximately 600 nm. In the embodiment shown inFIG. 3 said second coating material is a coating material as specifiedin the Linos Photonics catalog, 2001, section thin film coatings, pageH14, item FLP-5. This coating has an edge wavelength of approximately900 nm, so that the second coating material has a relatively highreflection coefficient for wavelengths below approximately 900 nm and arelatively low reflection coefficient for wavelengths aboveapproximately 900 nm. Since all portions of the light generated by theradiation source 9 are reflected at least once by the upper inner wall53 and at least once by the lower inner wall 55, a major portion of thelight having wavelengths below approximately 600 nm will be absorbed bysaid first portion 57 of the reflecting surface, a major portion of thelight having wavelengths above approximately 900 nm will be absorbed bysaid second portion 59 of the reflecting surface, and a major portion ofthe light having wavelengths between approximately 600 nm and 900 nmwill be reflected by both said first and said second portion 57, 59 ofthe reflecting surface and will consequently be transmitted by theradiation filter of the device 51. Thus said first and said secondreflection spectrum of, respectively, said first and said second portion57, 59 of the reflecting surface together match a predeterminedtransmission spectrum of the radiation filter of the device 51 whichroughly corresponds with the transmission spectrum of the radiationfilter of the device 1.

The embodiments of a device 1, 31, 51 for treating human skin inaccordance with the invention shown in FIGS. 1, 2, 3 and describedhereinbefore are devices for removing hairs from human skin, inparticular epilators for removing the hairs for a relatively long timeor even permanently. It is noted, however, that the invention alsoincludes other types of devices for treating human skin by means ofradiation. Examples of such devices are devices for the medical orcosmetic treatment by means of radiation or radiation pulses ofbirthmarks present on the skin, such as naevus vinosus and naevuspigmentosus, psoriasis, or aberrations of blood vessels present in theskin, such as varicose veins. It will be understood that a personskilled in the art of such treatments of the human skin knows or will beable to establish which kind of radiation, and in particular whichwavelengths of the radiation, is most effective for a particular kind oftreatment and which wavelengths are not effective and harmful to theremaining part of the skin. On the basis of this information a personskilled in the art of optics will be able to establish in astraightforward manner the predetermined transmission spectrum of theradiation filter and to find a suitable coating or combination ofcoatings providing a reflection spectrum which matches saidpredetermined transmission spectrum.

It is further noted that in the description and the claims theexpression “reflecting surface” is to be read in its proper context. Aperson skilled in the art will understand that, if reference is made tothe portion of the light reflected by the reflecting surface, it is thecoating that actually reflects said portion of the light. A personskilled in the art will also understand that, if reference is made tothe portion of the light absorbed by the reflecting surface, the coatingtransmits said portion of the light and said portion of the light isactually absorbed by, for example, the wall, substrate or otherstructure on which the coating is provided. The invention also coversembodiments in which said portion of the light is directly absorbed bythe cooling fluid of a cooling system. In such an embodiment, forexample, the coating is provided on a light transmitting substrate, suchas transparent glass, along which the cooling fluid flows.

In the embodiments shown in FIGS. 1, 2 and 3 the radiation paths 15,15′, 15″ are air or gas-filled. It is finally noted that the inventionalso encloses embodiments in which the radiation path is filled with afluid or in which the radiation path is even solid. Thus, for example,the radiation path may comprise a glass body through which the radiationpropagates, the surface of the glass body being provided with a coatingproviding the surface of the glass body with the desired reflectionspectrum for the radiation.

1. A device for treating human skin through the use of radiation, whichdevice comprises a housing with a radiation exit opening, a radiationsource accommodated in the housing, and a radiation path between theradiation source and the radiation exit opening, said radiation pathcomprising a radiation filter having a predetermined transmissionspectrum, wherein the radiation filter comprises a reflecting surfacevia which the radiation propagating along the radiation path isreflected and which has a coating providing the reflecting surface witha reflection spectrum substantially matching the predeterminedtransmission spectrum, wherein the radiation filter comprises a channelwhich encloses the radiation path and which comprises an inner wall onwhich the reflecting surface is provided, and wherein the channelcomprises a bend situated between the radiation source and the radiationexit opening.
 2. The device as claimed in claim 1, wherein thereflecting surface comprises a first portion, which has a first coatingmaterial providing said first portion with a first reflection spectrum,and a second portion, which has a second coating material providing saidsecond portion with a second reflection spectrum, said first and saidsecond reflection spectrum together matching the predeterminedtransmission spectrum.
 3. The device as claimed in claim 1, wherein thereflecting surface is provided on a wall which is in thermal contactwith a cooling system.
 4. The device as claimed in claim 3, wherein thecooling system comprises a circuit filled with a cooling fluid, the wallbeing in thermal contact with said circuit.
 5. The device as claimed inclaim 3, wherein the cooling system comprises a fan for generating a gasstream and a guide for guiding said gas stream along the wall.
 6. Thedevice as claimed in claim 1, wherein the device is a device forremoving hairs from human skin, wherein the radiation source is a flashlamp.
 7. A device for treating human skin through the use of radiation,which device comprises a housing with a radiation exit opening, aradiation source accommodated in the housing, and a radiation pathbetween the radiation source and the radiation exit opening, saidradiation path comprising a radiation filter having a predeterminedtransmission spectrum, wherein the radiation if filter comprises areflecting surface via which the radiation propagating along theradiation path is reflected and which has a coating providing thereflecting surface with a reflection spectrum substantially matching thepredetermined transmission spectrum, wherein the reflecting surfacecomprises a first portion, which has a first coating material providingsaid first portion with a first reflection spectrum, and a secondportion, which has a second coating material providing said secondportion with a second reflection spectrum, said first and said secondreflection spectrum together matching the predetermined transmissionspectrum.
 8. The device as claimed in claim 7, wherein the radiationfilter comprises a channel which encloses the radiation path and whichcomprises an inner wall on which the reflecting surface is provided. 9.The device as claimed in claim 8, wherein the channel comprises a bendsituated between the radiation source and the radiation exit opening.10. The device as claimed in claim 7, wherein the reflecting surface isprovided on a wall which is in thermal contact with a cooling system.11. The device as claimed in claim 10, wherein the cooling systemcomprises a circuit filled with a cooling fluid, the wall being inthermal contact with said circuit.
 12. The device as claimed in claim10, wherein the cooling system comprises a fan for generating a gasstream and a guide for guiding said gas stream along the wall.
 13. Thedevice as claimed in claim 7, wherein the device is a device forremoving hairs from human skin, wherein the radiation source is a flashlamp.